31 research outputs found
Switching the sign of Josephson current through Aharonov-Bohm interferometry
We investigate the DC Josephson effect in a superconductor-normal
metal-superconductor junction where the normal region consists of a ballistic
ring. We show that a fully controllable -junction can be realized through
the electro-magnetostatic Aharonov-Bohm effect in the ring. The sign and the
magnitude of the supercurrent can be tuned by varying the magnetic flux and the
gate voltage applied to one arm, around suitable values. The implementation in
a realistic set-up is discussed.Comment: 4 pages, 3 figure
Magnetic interference patterns in superconducting junctions: Effects of anharmonic current-phase relations
A microscopic theory of the magnetic-field modulation of critical currents is
developed for plane Josephson junctions with anharmonic current-phase
relations. The results obtained allow examining temperature-dependent
deviations of the modulation from the conventional interference pattern. For
tunneling through localized states in symmetric short junctions with a
pronounced anharmonic behavior, the deviations are obtained and shown to depend
on distribution of channel transparencies. For constant transparency the
deviations vanish not only near Tc, but also at T=0. If Dorokhov bimodal
distribution for transparency eigenvalues holds, the averaged deviation
increases with decreasing temperature and takes its maximum at T=0.Comment: 6 pages, 6 figure
Half-Periodic Josephson Effect in an s-Wave Superconductor - Normal Metal -d-Wave Superconductor Junction
We predict that the Josephson current in a clean s-wave superconductor-normal
metal-d-wave superconductor junction is periodic in superconducting phase
difference with period instead of . The frequency of
non-stationary Josephson effect is correspondingly The
effect is due to coexistence in the normal layer of current carrying Andreev
levels with phase differences and Comment: 4 pages, REVTeX, 3 figure
Gauge-invariant electromagnetic response of a chiral px+ipy superconductor
We present a gauge-invariant theory of the electromagnetic response of a
chiral px+ipy superconductor in the clean limit. Due to the spontaneously
broken time-reversal symmetry, the effective action of the system contains an
anomalous term not present in conventional superconductors. As a result, the
electromagnetic charge and current responses contain anomalous terms, which
depend explicitly on the chirality of the superconducting order parameter.
These terms lead to a number of unusual effects, such as coupling of the
transverse currents to the collective plasma oscillations and a possibility of
inducing the charge density by the magnetic field perpendicular to the
conducting planes. We calculate the antisymmetric part of the conductivity
tensor (the intrinsic Hall conductivity) and show that it depends on the wave
vector of the electromagnetic field. We also show that the Mermin-Muzikar
magnetization current and the Hall conductivity are strongly suppressed at high
frequencies. Finally, we discuss implications of the theory to the experiments
in Sr2RuO4.Comment: 22 pages, 4 figures, final version as published in PR
Dephasing in Disordered Conductors due to Fluctuating Electric Fields
We develop a novel eikonal expansion for the Cooperon to study the effect of
space- and time-dependent electric fields on the dephasing rate of disordered
conductors. For randomly fluctuating fields with arbitrary covariance we derive
a general expression for the dephasing rate which is free of infrared
divergencies in reduced dimensions. For time-dependent external fields with
finite wavelength and sufficiently small amplitude we show that the dephasing
rate is proportional to the square root of the electromagnetic power coupled
into the system, in agreement with data by Wang and Lindelof [Phys. Rev. Lett.
{\bf{59}}, 1156 (1987)].Comment: 17 Latex-pages, one figure; we now give more technical details and
discuss the screening problem more carefully; to appear in Phys. Rev.
Anharmonic Josephson current in junctions with an interface pair breaking
Planar superconducting junctions with a large effective Josephson coupling
constant and a pronounced interface pair breaking are shown to represent weak
links with small critical currents and strongly anharmonic current-phase
relations. The supercurrent near Tc is described taking into account the
interface pair breaking as well as the current depairing and the Josephson
coupling-induced pair breaking of arbitrary strengths. A new analytical
expression for the anharmonic supercurrent, which is in excellent agreement
with the numerical data presented, is obtained. In junctions with a large
effective Josephson coupling constant and a pronounced interface pair breaking,
the current-induced depairing is substantially enhanced in the vicinity of the
interface thus having a crucial influence on the current-phase relation despite
a small depairing in the bulk.Comment: 5 pages, 2 figures, published versio
Gauge-fixing parameter dependence of two-point gauge variant correlation functions
The gauge-fixing parameter dependence of two-point gauge variant
correlation functions is studied for QED and QCD. We show that, in three
Euclidean dimensions, or for four-dimensional thermal gauge theories, the usual
procedure of getting a general covariant gauge-fixing term by averaging over a
class of covariant gauge-fixing conditions leads to a nontrivial gauge-fixing
parameter dependence in gauge variant two-point correlation functions (e.g.
fermion propagators). This nontrivial gauge-fixing parameter dependence
modifies the large distance behavior of the two-point correlation functions by
introducing additional exponentially decaying factors. These factors are the
origin of the gauge dependence encountered in some perturbative evaluations of
the damping rates and the static chromoelectric screening length in a general
covariant gauge. To avoid this modification of the long distance behavior
introduced by performing the average over a class of covariant gauge-fixing
conditions, one can either choose a vanishing gauge-fixing parameter or apply
an unphysical infrared cutoff.Comment: 21 pages, RevTe